The weight number seems like a good one to me. The lowest I ever get out door with is about 45lbs and the most is almost 3 times that. How much gear one takes is a function of many variables but it all comes down to a personal decision of what is right to take - there isn't a good or bad answer. If you have what you need when you need it - it's good. After a few tours one learns what can be left at home or what needs to be included.
With respect to daily distance, 100km seems reasonable, though you may want to increase the distance you're riding before you depart to get ready for higher distances once on tour. You might consider putting weight in your panniers even when riding around town, doing errands, etc. to get used to the feel of the bike loaded. As you increase your daily distance it becomes more important to be sure you're meeting your nutrition, hydration and electrolyte needs.
I have no clue on getting from Los Angeles to Chihuaha (Northern Mexico).